The present invention relates to apparatus and methods for treating workpieces with ultrasonic energy. More specifically, the present invention relates to apparatus and methods for performing ultrasonic cleaning of workpieces having a pair of opposed, planar surfaces, for example, disc-shaped workpieces. The invention has particular utility in the manufacture of disc-shaped magnetic and magneto-optic (xe2x80x9cMOxe2x80x9d) recording media and semiconductor devices employing semiconductor wafer substrates.
The ever-increasing areal recording densities of magnetic and MO recording media, as in the form of discs, results in continued reduction in the sizes of critical defects formed during the manufacturing process, which necessitate removal of particles having sizes (i.e., diameters) below about 0.5 xcexcm. According to conventional practices utilizing ultrasonic and/or megasonic techniques for treating, e.g., cleaning, desmutting, etc., of such disc-shaped workpieces as are utilized as layer deposition substrates in the manufacture of various types of magnetic and MO recording media, as well as semiconductor integrated circuit (IC) devices processed from a single semiconductor wafer substrates, a plurality of discs are simultaneously processed in an ultrasonic tank in batches. Conventional ultrasonic apparatus for performing such batch cleaning operations typically comprise a stainless steel tank or vessel with several ultrasonic transducers attached to the bottom thereof. The ultrasonic transducers are driven by generators so as to vibrate at ultrasonic frequencies (xcx9c20-500 kHz) that create pressure waves in the cleaning liquid contained within the tank or vessel, which pressure waves in turn remove contaminants, particulate matter, etc., from the workpiece surfaces by different mechanisms. A simplified, schematic top plan view of a typical bottom-mounted transducer ultrasonic cleaning apparatus 10 comprising a rectangularly-shaped stainless steel tank 1 having a plurality of vertically oriented workpieces 2, e.g., discs, each having opposed, planar surfaces 2a and 2b, is shown in FIG. 1. The major advantage of the conventional batch method is that typically ca. 100-150 workpieces can be processed in about 300-360 sec.
However, such batch processing techniques utilizing bottom-mounted transducer ultrasonic cleaning apparatus as illustrated in FIG. 1 incur several disadvantages and drawbacks, including:
(1) the intensity of the ultrasonic (i.e., acoustic) energy field that a surface of a particular workpiece experiences is different for each disc, primarily as a result of the geometric arrangement of the discs and significant variation in the acoustic energy across the bottom of the tank or vessel, for example, arising from the formation of standing (or stationary) acoustic waves rather than progressive (or traveling) waves. For example, FIG. 2 illustrates the large variation in transmitted acoustic energy (measured in terms of power density, watts/unit area) across the bottom surface of a conventional ultrasonic apparatus employing a plurality of bottom-mounted ultrasonic transducers; and
(2) the relatively large tanks or vessels of conventional batch-type ultrasonic treatment apparatus contain a considerable amount of cleaning liquid or bath, which liquid bath is, on average, utilized for a very long interval, typically about 10-12 hours, before being replaced with fresh cleaning solution. However, as the workpieces (e.g., discs) are processed in the tank, particulate matter and other contaminants, such as soluble and/or insoluble materials, are removed from the workpiece surfaces and become suspended and/or dissolved in the cleaning solution, thereby increasing the likelihood of particle redeposition, damage to the workpiece surfaces arising from the mechanical abrading action exerted thereon by the suspended particles, and a general reduction in effectiveness of the cleaning/removal properties of the cleaning bath or solution due to exhaustion of the active ingredients or components thereof, e.g., surfactants, detergents, etc. As a consequence, in order to extend the effectiveness of the cleaning solution, the latter is typically recirculated through a filter, which filter has a further disadvantage of incurring contaminant loading necessitating periodic cleaning and/or replacement of the filter material or cartridge.
Accordingly, there exists a clear need for improved apparatus and methodology for performing simple, reliable, rapid, and cost-effective ultrasonic treatment of workpieces, e.g., disc-shaped workpieces used as deposition substrates in the manufacture of magnetic and/or MO recording media and semiconductor wafer substrates utilized in the fabrication of semiconductor IC devices, which apparatus and methodology avoids the drawbacks and disadvantages associated with use of the conventional, batch-type, bottom transducer-mounted ultrasonic devices, and provides, inter alia, single-disc ultrasonic processing where each disc is subjected to the same amount/intensity of acoustic energy providing equal removal forces; relatively small tank or vessel sizes facilitating rapid and frequent cleaning bath replacement, filtering, or replenishment; elimination of xe2x80x9cdead spacesxe2x80x9d of very low acoustic power within the tank or vessel due to reduction or elimination of disadvantageous stationary wave formation and enhanced formation of progressive waves; obtainment of production economies resulting from lower cost and maintenance of a bank of relatively small ultrasonic tanks operating in parallel, vis-à-vis a single large tank; and smaller impact on product throughput than which results upon malfunction of a single large tank.
The present invention, wherein the reflection and transmission characteristics of ultrasonic waves supplied to a liquid contained in a relatively small chamber or tank via a sidewall-mounted transducer and simultaneously applied to the opposing surfaces of a single planar workpiece, e.g., a disc-shaped workpiece such as a deposition surface of a substrate for a magnetic or MO recording medium or a semiconductor wafer, are manipulated to locally increase the acoustic power density and/or formation of progressive waves, effectively addresses and solves the above-stated need for improved methodology and instrumentalities for performing ultrasonic treatment of planar-surfaced workpieces. Further, the methodology and apparatus provided by the instant invention can be implemented in a cost-effective manner utilizing readily available materials and components, and the methodology and apparatus afforded by the present invention enjoy diverse utility in the manufacture of numerous types of manufacturing processes in addition to those specifically enumerated.
An advantage of the present invention is an improved apparatus for treating surfaces of a single workpiece with ultrasonic energy.
Another advantage of the present invention is an improved apparatus for treating a single workpiece having a pair of opposed, planar surfaces with ultrasonic energy.
Yet another advantage of the present invention is an improved method for treating surfaces of a single workpiece with ultrasonic energy.
Still another advantage of the present invention is an improved method for treating a single workpiece having a pair of opposed, planar surfaces with ultrasonic energy.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by an apparatus for treating surfaces of a single workpiece with ultrasonic energy, comprising:
(a) a chamber defining an interior space for containing therein a liquid, the chamber comprising a bottom wall and a first pair of opposing, longitudinally extending sidewalls connected by a second pair of opposing, transversely extending sidewalls;
(b) an ultrasonic wave energy applying means for supplying ultrasonic wave energy to a liquid contained within the interior space of the chamber, the ultrasonic wave energy applying means including a planar transducing surface forming at least a portion of a first one of the second pair of opposing, transversely extending sidewalls; and
(c) a workpiece mounting means within the interior space of the chamber for mounting therein a single workpiece, the workpiece mounting means comprising means for mounting a single workpiece comprising a pair of opposed, planar surfaces, such that the pair of opposed, planar surfaces are oriented perpendicularly to the planar transducing surface of the ultrasonic wave energy applying means for simultaneously receiving therefrom ultrasonic energy.
In embodiments according to the present invention, the workpiece mounting means (c) comprises means for mounting a disc-shaped substrate; and the apparatus further comprises an acoustic waveguide means at least partially surrounding the planar transducing surface of the ultrasonic wave energy applying means for increasing the power density of ultrasonic energy supplied to the liquid.
According to embodiments of the invention, the apparatus further comprises ultrasonic energy reflecting means located within the interior space; and movable partition means transversely extending at least partway between the first pair of opposing, longitudinally extending sidewalls for adjustably partitioning the interior space into first and second sub-spaces each extending for a desired, adjustable length along the first pair of longitudinally extending sidewalls, the movable partition means being comprised of a material (e.g., a sheet of a polyurethane material) which is partially reflective and partially transmissive of ultrasonic wave energy; and the workpiece mounting means (c) is adapted to be selectively positioned within either the first sub-space or the second sub-space.
According to an embodiment of the present invention, the ultrasonic energy reflecting means comprises the second one of the second pair of transversely extending, opposing sidewalls for reflecting ultrasonic energy back to the movable partition means; whereas according to another embodiment of the present invention, the ultrasonic energy reflecting means comprises a contoured surface ultrasonic reflector for reflecting ultrasonic energy away from the movable partition means and onto an ultrasonic energy absorbing means located within the interior space, thereby increasing the formation of progressive ultrasonic energy waves within the interior space while decreasing the formation of standing ultrasonic energy waves.
According to further embodiments of the present invention, the apparatus further comprises workpiece supplying/withdrawal means for inserting the workpiece mounting means into the interior space and for withdrawing the workpiece mounting means from the interior space after a predetermined interval for treatment of a workpiece; and a liquid supply means including recirculation and filter means for recirculating and filtering liquid contained in the chamber and/or for supplying fresh liquid to the chamber.
According to another aspect of the present invention, a system for treating a plurality of workpieces each having a pair of opposed, planar surfaces comprises a plurality of the above-described ultrasonic energy treating apparatuses fluidly connected in parallel.
According to yet another aspect of the present invention, a method of treating a single workpiece having a pair of opposed, planar surfaces with ultrasonic energy comprises the steps of:
(a) providing an apparatus comprising:
(i) a chamber having an interior space containing therein a liquid, the chamber comprising a bottom wall and a first pair of opposing, longitudinally extending sidewalls connected by a second pair of opposing, transversely extending sidewalls;
(ii) an ultrasonic wave energy applying means for supplying ultrasonic energy to the liquid in the chamber, the ultrasonic wave energy applying means including a planar transducing surface forming at least a portion of a first one of the second pair of opposing, transversely extending sidewalls; and
(iii) a workpiece mounting means positioned within the interior space of the chamber for mounting therein a single workpiece comprising a pair of opposed, planar surfaces, such that the pair of surfaces are oriented perpendicularly to the planar transducing surface at a preselected spacing therefrom;
(b) positioning within the interior space a workpiece mounting means having a single workpiece, such that each of the pair of workpiece surfaces is in contact with the liquid; and
(c) applying ultrasonic energy from the planar transducing surface to the liquid for simultaneous treatment of each of the pair of workpiece surfaces.
According to embodiments of the present invention, step (c) further includes reflecting ultrasonic energy applied from the planar transducing surface to the liquid via reflective means located within the interior space; and step (a)(i) further comprises providing a movable partition means within the interior space, the movable partition means extending transversely at least partway between the first pair of opposing, longitudinally extending sidewalls for adjustably partitioning the interior space into a first sub-space including the planar transducing surface and a second sub-space including the second one of the second pair of opposing, transversely extending sidewalls, each of the first and second sub-spaces extending for a desired, adjustable length along the first pair of longitudinally extending sidewalls, the movable partition means being comprised of a material which is partially reflective and partially transmissive of ultrasonic energy; and step a(iii) further comprises positioning the workpiece mounting means in either the first sub-space or the second sub-space at a spacing from the transducing surface which provides the pair of substrate surfaces with a desired amount of ultrasonic power.
According to an embodiment of the present invention, step (c) comprises reflecting the ultrasonic energy back to the movable partition means; whereas according to another embodiment of the present invention, step (c) comprises reflecting the ultrasonic energy away from the movable partition means and onto an ultrasonic energy absorbing means located within the interior space, thereby increasing the formation of progressive ultrasonic waves within the interior space while decreasing the formation of standing ultrasonic waves.
According to particular embodiments of the present invention, step (a)(i) comprises providing a movable partition means comprising a sheet of a polyurethane or other suitable material; step (a)(iii) comprises positioning said workpiece mounting means within the second sub-chamber; and step (b) comprises providing a disc-shaped substrate.
According to still another aspect of the present invention, an apparatus for treating surfaces of a single workpiece with ultrasonic energy comprises:
(a) a chamber comprising a bottom and a plurality of pairs of planar sidewalls, the chamber including a planar ultrasonic transducing surface forming at least a portion of one of the sidewalls; and
(b) means for mounting a single workpiece having a pair of opposed, planar surfaces such that the pair of surfaces are oriented perpendicularly to the planar ultrasonic transducing surface.
According to embodiments of the present invention, the apparatus further comprises:
(c) movable partition means within the chamber for adjustably partitioning the chamber into two sub-chambers and comprised of a material which is partially reflective and partially transmissive of ultrasonic wave energy; and
(d) reflector means within the chamber for reflecting ultrasonic wave energy back to the partition means or to an ultrasonic energy absorber located within the chamber.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.